Plasma catecholamines and response to exercise in 6-hydroxydopamine-treated dogs

Abstract

Plasma catecholamine (CA; picograms per millilitre) concentrations were measured simultaneously with heart rate (HR, beats per minute) during short-duration exercise, and with plasma glucose, lactate, and free fatty acid (FFA) concentrations (millimoles per litre) during long-duration exercise, in control dogs (N-dogs) and in sympathectomized dogs (S-dogs) with 6-hydroxydopamine (50 mg∙kg−1). At rest, higher plasma CA in S-dogs (690 ± 90 vs. 320 ± 60) was associated with higher HR (126 ± 3 vs. 90 ± 5), plasma glucose (6.4 ± 0.2 vs. 5.1 ± 0.2), lactate (2.9 ± 0.2 vs. 1.6 ± 0.2), and FFA concentrations (1.08 ± 0.11 vs. 0.81 ± 0.11). During short-duration exercise a normal HR response in S-dogs (226 ± 9 vs. 228 ± 8) was dependent upon larger than normal plasma CA values (4280 ± 680 vs. 1990 ± 360). Metabolic adjustments to long-duration exercise were impaired in S-dogs as evidenced by the higher plasma glucose and lactate concentrations (8.2 ± 0.5 and 5.5 ± 0.3 vs. 6.4 ± 0.4 and 4.6 ± 0.3) and the lower plasma FFA concentration (0.66 ± 0.16 vs. 1.20 ± 0.09). These occurred despite a normal plasma CA response in S-dogs (6850 ± 1450 vs. 8740 ± 1680). Following chemical sympathectomy the adrenal medulla can compensate to ensure an adequate heart rate response to short-duration exercise, but not to ensure adequate metabolic adjustments to prolonged exercise.